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  Java Practices -> Beware multilingual submit buttons
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<div class='page-title'>Beware multilingual submit buttons</div>

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<br>When multiple&nbsp;<tt>SUBMIT</tt> controls are used in an HTML form,
it is natural to use this style :
<p><tt>&lt;input type="submit" name="operation" value="Add">
<br>&lt;input type="submit" name="operation" value="Change">
<br>&lt;input type="submit" name="operation" value="Delete"></tt>
<p>Here, the server detects the desired operation by simply examining the
value of the&nbsp;<tt>operation</tt> parameter.
<p>However, this style does not work well when the application is multilingual,
since the&nbsp;<tt>value</tt> attribute varies according to language.
<p>A simple workaround for this problem is to use a different name for
each&nbsp;<tt>SUBMIT</tt> control :
<p><tt>&lt;input type="submit" name="operation_Add" value="Add">
<br>&lt;input type="submit" name="operation_Change" value="Change">
<br>&lt;input type="submit" name="operation_Delete" value="Delete"></tt>
<p>Here, the server will detect the desired operation by looking for the
<i>presence</i> of certain parameter names, and not by examining the value
of a single&nbsp;<tt>operation</tt> parameter.
<p>An application might define a naming convention to ease the extraction
of the desired operation. Here is an example method where request parameters
whose names start with&nbsp;<tt>operation_</tt> are treated as operation
indicators. This method may be placed in a base action class, or in a utility
class :
<br>
<PRE>

<span class='keyword'>import</span> java.util.*;
<span class='keyword'>import</span> javax.servlet.http.HttpServletRequest;
<span class='keyword'>import</span> java.util.logging.*;

<span class='keyword'>public</span> <span class='keyword'>final</span> <span class='keyword'>class</span> SubmitOperation {

 <span class='comment'>/**
  * Determine the desired operation.
  *
  * Returns the name of the single submitted operation_X parameter, without
  * the leading 'operation_'. For example, if a single parameter named
  * operation_Add is present in aRequest, then this method will return
  * 'Add'.
  *
  * This method depends on two conventions :
  * &lt;ul&gt;
  * &lt;li&gt;a naming convention, whereby the names of request parameters which
  * denote an operation are in the style : 'operation_blah', 'operation_XYZ',
  * and so on. That is, the parameter name starts with 'operation_'
  * &lt;li&gt;at most one operation_X parameter can appear in aRequest
  * (it may have none; in that case this method will return null).
  * &lt;/ul&gt;
  *
  * This method is needed only when the app is multilingual, and
  * multiple SUBMIT buttons appear on a single page.
  */</span>
  String getOperation(HttpServletRequest aRequest){
    String result = <span class='keyword'>null</span>;
    String OPERATION = <span class='literal'>"operation_"</span>;
    List operationParamNames = <span class='keyword'>new</span> ArrayList();
    Enumeration allParamNamesEnum = aRequest.getParameterNames();
    <span class='keyword'>while</span> ( allParamNamesEnum.hasMoreElements() ) {
      String paramName = (String)allParamNamesEnum.nextElement();
      <span class='keyword'>if</span> ( paramName.startsWith(OPERATION) ) {
        operationParamNames.add(paramName);
      }
    }
    <span class='keyword'>if</span> ( ! operationParamNames.isEmpty() ) {
      <span class='keyword'>if</span> ( operationParamNames.size() &gt; <span class='literal'>1</span> ) {
        <span class='keyword'>throw</span> <span class='keyword'>new</span> IllegalArgumentException(
          <span class='literal'>"Expecting at most one parameter starting with '"</span> + OPERATION +
          <span class='literal'>"'. Actually found : "</span> + operationParamNames
        );
      }
      String operationParamName = (String)operationParamNames.get(<span class='literal'>0</span>);
      result = operationParamName.substring(OPERATION.length());
    }
    fLogger.fine(<span class='literal'>"Operation : "</span> + result);
    <span class='keyword'>return</span> result;
  }

  <span class='comment'>// PRIVATE //
</span>  <span class='keyword'>private</span> <span class='keyword'>static</span> <span class='keyword'>final</span> Logger fLogger = Logger.getLogger(
    SubmitOperation.<span class='keyword'>class</span>.getName()
  );
} 
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<div class='topic-section'>See Also :</div>
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  <a href='TopicAction5422-2.html?Id=218'>Understand details of FORM tags</a> <br>
 
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